This R13 conference grant application requests funds to support the XXIIIrd North American Testis Workshop that will be held from April 15 to April 18, 2015 in Salt Lake City, Utah. Since 1972, the North American Testis Workshop has been the premiere international forum for bringing basic and clinician-scientists together to present and discuss the most recent findings on the regulation and function of the fertile and infertile testis The first goal of this meeting is to promote solutions for two major medical and public health problems: the high incidence of male infertility in the developed world and the lack of a safe and reversible male contraceptive. Another important goal of this meeting is to foster the development of future leaders in this field, especially if they currently are trainees, or if they re women or underrepresented minorities. The theme of the XXIIIrd North American Testis Workshop is, Health Sperm-Healthy Children. The program includes four major lectures: the keynote address, and three benchmark lectures from international speakers. There also will be 17 invited talks, which are grouped in six sessions. Session 1 is: Male Fertility Across Generations - Setting the Stage; Session 2 is: Healthy Stem Cells, Healthy Aging; Session 3 is: Regulation of Gene Expression from Progenitor Cells through Meiosis; Session 4 is: Determining and Perturbing Testicular Function; Session 5 is: Somatic Cells; and Session 6 is: Human Fertility, Infertility and the Next Generation. In addition to the invited talks, each session will end with to short talks from abstracts that are submitted by young investigators (trainees and Assistant Professors who have been in rank for no more than 2 years.) The meeting also includes two poster sessions, and the posters will remain on display throughout the meeting. The keynote address begins the meeting and sets its tone. Dr. Amander Clark, from the Department of Molecular, Cell and Developmental Biology at the University of California in Los Angeles will present this lecture. Dr. Clark is an engaging, motivating lecturer and one of the world's leading experts in the study of human primordial germ cells. Abnormal development of the early germ cell lineage can result in infertility, germ cell tumor formation or result in birth defects in the offspring. Her talk provides a foundation for many of the talks throughout the meeting especially those on germ cells and their unique genetic and epigenetic programs. Furthermore, the keynote address links well with the final session of the meeting on human fertility. The first benchmark lecture highlights major advances in our understanding of primate spermatogonial stem cells and their clinical applications. Dr. Stefan Schlatt, Professor at the University of Muenster, Germany, is internationally recognized for his research using of the non-human primate model in the study of spermatogenesis and spermatogonia. His talk will provide a strong foundation for Session 2. Professor Sarah Robertson of the University of Adelaide in Australia will present the second benchmark lecture addressing how factors in seminal fluid can interact with the maternal uterine environment to influence the metabolic phenotype of the offspring, a dramatic example of paternally-mediated intergenerational effects, a topic that is also addressed in Session 1. The third benchmark lecture will be delivered by Professor Lee Smith from the MRC Centre for Reproductive Health at the University of Edinburgh. Professor Smith's group specializes in identifying genetic and hormonal control signals that support male fertility and steroid hormone (testosterone) production. His topic links not only to basic topics in sessions 2 and 5 but also focuses on the important question of how androgen production is controlled in the testis and how this influences male fertility. In this application, we request funds to partially defray the cst of attendance of the 10 young investigators whose abstracts will be selected for short platform talks. The rest of the funds will defray part of the housing costs for the 21 distinguished scientists who have been invited to speak at this meeting.